Qos Capability Support for PCF and SMF Interaction

SMF supports Diff-Serv-Code-Point (DSCP) or Type of Service (ToS) QoS functions during interaction with PCF. Traffic defined at SMF can be prioritized based on the tosTrafficClass value that SMF receives from PCF. Using the ToS values provided, UPF performs DSCP packet match in the downlink direction and UE performs DSCP packet match in the uplink direction. This feature allows packet matching using ToS values, even if no FlowDescription values exist.

The following functions enable this feature:

• PCF sends tosTrafficClass IE which is part of FlowInformation within the PCC rule from PCF. SMF decodes it and stores it as part of the respective QoS Flow.

• SMF populates the tosTrafficClass IE value received from PCF in the tosTrafficClass inside SDF IE within PDI while creating the downlink PDR.

• Support for tosTrafficClass toward UE.

The following call flow describes the flow from PCF to SMF to support tosTrafficClass IE:

• You can deploy basic PCF which supports minimal functionality. The PCF need not support northbound interfaces and installs dedicated flows which are based on local configuration.

• UE only creates a single session (default bearer) to support data, voice, and video. PCF triggers four flows during PDU session creation, one each for voice, video, data, and network management.

• PCF based on local configuration sends four PCC rules each with FlowInformation carrying tosTrafficClass IE in the N7 create response.

• SMF supports flow creation for PCC rules mapped with FlowInformation having only tosTrafficClass and no FlowDescription.

• PCF may include FlowDescription within FlowInformation with filters, such as permit in IP from any to any or permit out IP from any to any.

• PCF includes QoS Data in smPolicyDecision for each of the pcc rules indicating the associated QCI. SMF creates QoS Flow for each of the QCI.

• SMF includes tosTrafficClass inside SDF IE in the downlink PDR in N4SessionEstablishmentReq to UPF while installing the rules from PCF with mapped tosTrafficClass.

• SMF sends the N1 PDU establishment response to PCF. This response includes details, such as QoS rules containing packet filters that are configured with type of service or traffic class type, based on the information that is received from PCF. If the SMF doesn't receive the flow direction from PCF, packet filter direction is populated as bidirectional and packet filter component type identifier is populated as Type of service or Traffic class type.